Precision polymer network science with tetra-PEG gelsa decade history and future

Tetra-PEG gels, near-ideal polymer networks prepared by cross-end-coupling of A and B tetra-functional poly(ethylene glycol) (PEG) prepolymers having complementary end groups, were first fabricated in 2008. Comparisons of the mechanical properties with those of theoretical predictions indicate negligible fractions of defects and/or entanglements. Small-angle neutron scattering profiles of Tetra-PEG gels are very similar to those of the corresponding polymer solutions, suggesting negligible inhomogeneities originated from cross-linking. Due to the remarkable mechanical properties, extremely low structural inhomogeneities, and biocompatibility, tetra-PEG gels have gathered much attention since its discovery. The number of citation of Tetra-PEG gels is now over 2700 and is still growing rapidly. Chemical reaction kinetic studies also show a high degree of cross-linking reaction and its tunability, which leads to an idea of cross-linking probability tuned (p-tuned) networks. Versatility of the cross-coupling reactions allows us to prepare not only hydrogels but also organogels and ion gels, copolymer gels, non-stoichiometric gels, and so on. A decade history of the Tetra-PEG gels is reviewed with a variety of potential applications encompassing multiresponsive systems.